Methods of preparation of cyclohexadienes



METHODS OF PREPARATION OF CYCLOHEXADIENES Alfred Viola, College Park, Md., Herman Fleischacker, Washington, D. (1., Gilbert Forrest Woods, Silver Spring, Md., and Nicholas Charles Eoigiano, Pittsburgh, Pa.

No Drawing. Application March 10, 1955 Serial N 0. 493,576

4 Claims. (Cl. 260-666) This invention relates to methods of preparation of cyclohexadienes. More particularly, the invention relates to methods of preparation of cyclohexadienes by the cyclization of dienols. The invention further relates to the preparation of cyciohexadienes such as methylcyclohexadiene, dimethylcyclohexadiene, phenylcyclohexadiene, and the like.

The aforementioned cyclohexadienes may readily be converted to the corresponding aromatic equivalents, for example, by conversion of l,4-dimethylcyclohexadiene to p-xylene as illustrated hereinafter.

The present invention contemplates the catalytic cyclization of alkyl-, polyalkyl-, or aryl-dienols with the loss of the elements of water to substituted cyclohexadienes at elevated temperatures. For convenience the term cyclization will be construed hereinafter to mean dehydrocyclization (cyclization with loss of water).

Alumina, silica, clays and the like are found to be efiective catalysts for the aforementioned cyclization.

Cyclization temperatures for optimum yields range from above 306 C. and greatly improved yields are manifested at temperatures of 400 C. and above.

Without intending to limit the scope of the patent thereto, the present invention will be illustrated by the following examples:

EXAMPLE I Preparation of phenylcyclohexadiene from 1' -phenyl 2 ,4 -h exadien-I -ol We observed that the yield of l-phenyl-lfij-hexa substance was obtained. Isolation of the new product by v the usual procedure of drying recrystallization from 3040 petroleum eth r yielded a white crystalline compound melting at 84-86. Uusually seven recrystallizations were necessary in order to obtain a substance whose melting point did not change appreciably on further recrystallization. Only four recrystallizations were necessary when the irnpure solid was allowed to stand in contact with air, since the soluble impurity (l-phenyl- 1,3,5-hexatriene) polymerized and would not dissolve in petroleum ether. Operating in this manner, phenylcyclohexadiene was obtained which was quite stable even when exposed to the air for several weeks.

Analysis.Calcd for C 3 C, 92.25; Found: C, 92.40; H, 7.79.

If, however, the alcohol, l-phenyl-ZA-hexadien-l-ol, is passed over alumina which is heated to a temperature in excess of that given above (32535 the amount of phenylcyclohexadiene isolated increases While the amount of l-phenyl-l,3,5-hexatriene decreases. Correspondingly, the difiiculty of isolation of phenylcyclohexadiene is markedly reduced.

2,836,630 Patented May 27, 1958 ice 2 EXAMPLE 11 EXAMPLE III Preparation of 1,4-dimetlzylcyclohexadiene from 2,5-

dimethylhexa-l,3-dien-5-0l 2,5-dimethylhexa-1,3-dien-5-ol (37 g.) was passed over alumina at a temperature above 350 (3., preferably 4%- 500 C., using reduced pressure and a nitrogen atmosphere. A yellow product (24 g.) was obtained in addition to water. Distillation of this material yielded 1,4- dimethylcyclohexadiene collected from 123130 C.

Analysis.-Caicd for C l-I C, 88.9%; H, 11.1%. Found: C, 88.7%; H, 11.2%. The ultraviolet absorption spectrum is a typical diene curve.

As an example of proof of structure of this substance, the dimethylcyclohexadiene (5.4 g.) was reacted with maleic anhydride (6.8 g.) in benzene (10 1111.). The product thus obtained (6.8 g.) Was isolated by distillation 115418 C./.1 mm. This material solidified and was recrystallized from petroleum ether; M. P. 5254 C.

Ai2alysis.Calcd for C I-L 0 C, 69.88; H, 6.84. Found: C, 69.92, H, 6.94.

This material is not the corresponding adduct from 2,5-dimethylhexatriene which melted at 117-1l9 C. The Diels-Alder adduct from 1,4-dimethylcyclohexadiene was catalytically hydrogenated to establish the number of ethylenic links remaining. The adduct (1.09 g.) dissolved in etroleum ether absorbed 130 ml. of hydrogen at 760 mm. and 26 C. This is also the value calculated for one ethylenic link.

To establish the existence of the C ring in the 1,4-dimethylcyclohexadiene claimed above, the 1,4-dimethylcyclohexadiene was converted to p-xylene; 10 g. of the cyclohexadiene was added dropwise to a flask which con tained approximately 1 g. of palladinized charcoal (10%) and which was fitted with a reflux condenser. The flask was heated by immersion in an oil bath, the temperature or" which was maintained at 200 during the addition and for a subsequent half hour. The product Was isolated by distillation (liquid) and was recrystallized from low boiling petroleum ether. The yield from such treatment was 2.5 g. The substance so obtained gave no depression of melting point with an authenic sample of p-xylene and had an identical ultraviolet absorption spectrum with that of p-xylene.

EXAMPLE IV been obtained by the addition of methyl magnesium from the third dienol mentioned above. The product in' the instance of Z-methyl-l,5-heXadien-3-o1 (the second' dienol) boiled at 24 -29? C./20-25 mm, 11 2144445.

A The ultraviolet absorption curves in each case showed typical conjugate diene absorption with small amounts 7 of the triple peak conjugate triene superimposed. 1 The I triene impurity was markedly decreased in each'case by raising the temperature, at which the catalytic reaction was carried out. V

Suitable modifications may be made in the foregoing examples without departing from the scope of the invention, as will be apparent to those skilled in the a1t.

It isintended that the patent shall cover by suitable expression in the'appended claims the features of patentable novelty residing in the invention.

We claim: 7 a

1. The method of preparation of cyclohexadienes comprising cyclizing, with loss of'water, a dienol having at least six carbon atoms at a temperature in excess of 300 C. in the vapor phase in the presence of an'inorganic solid 7 catalyst.

2. The method of preparation of substituted cyclohexadienes comprising cyclizing, with loss of water, an alkylhexadienol at a temperature n excess of 300 C. in the vapor phase in the presence of an inorganic solid catalyst. 3. The method of preparationof substituted cyclohexadienes comprising cyclizing; with loss of Water, a polyalkylhexadienol at a temperature in excess of 300 C. in the vapor phase in the presence of an inorganic solid catalyst. I i. III. V V

a 4. The method of preparation of substituted cyclohexadienes comprising cyclizing, with lossof water, arylhexa dienol at a temperature in excess'of 300 C. in the vapor phase in the presence of an inorganic solid catalystfl I References Cited in the file of this patent;

UNITED STATES PATENTS 1 2,406,530"

OTHER REFERENCES Woods at 51.: pp. 3394-96.

Woods et all: Jour. Chem. Soc. vo1. 77,?April' Fleischaclier et al.:,Jour;Am. Chem;Soc., v51. 78, 7

Butz et al.: Journal of Organic Chemistry, vol. "5, pages 171-183 (1939); lour. 1978 (1942). I v

Olberg et al.: I our; Am. Chem. Soc.; vol. 66, pp. 1096- 99 (1944). 1 i

Am; Chem. Soc., vol.. 64, page;

. Pines et-al. Aug. 27, 1946 loun'Am Chem. Soc., vet. to (1943 

1. THE METHOD OF PREPARATION OF CYCLOHEXADIENES COMPRISING CYCLIZING, WITH LOSS OF WATER, A DIENOL HAVING AT LEAST SIX CARBON ATOMS AT A TEMPERATURE IN EXCESS OF 300* C. IN THE VAPOR PHASE IN THE PRESENCE OF AN INORGANIC SOLID CATALYST. 